91Ó°ÊÓ

The particle along an x axis, first outward from to x=1.0cm and $x=4.0cm$then back to $x=1.0cm$, while an external force acts on it.

In an isolated system where any conservative force causes energy changes, the net work done by the system is zero for conservative forces.

Formula:

The work done by an applied force from one point to the other,$W={∫}_{ri}^{rf}{F}_{x}dx$ (i)

We can find the work done by using the given data in equation (i) as follows:

$$\begin{gathered} W={∫}_{ri}^{rf}3dx+{∫}_{ri}^{rf}-3dx \\ =\left[3x\right]\begin{array}{c}4\\ 1\end{array}+\left[-3x\right]\begin{array}{c}1\\ 4\end{array} \\ =3\left(4\right)-3\left(1\right)+\left(-3×1\right)-\left(-3×4\right) \\ =12-3-3+12 \end{gathered}$$

Solve further as:

$$\begin{gathered} W=9+9 \\ =18J \end{gathered}$$

Hence, the value of the work done is 18 J.

We can find the work done by using the given data in equation (i) as follows:

$$\begin{gathered} W={∫}_1^{4}5dx+{∫}_4^{1}5dx \\ =\left[5x\right]\begin{array}{c}4\\ 1\end{array}+\left[5x\right]\begin{array}{c}4\\ 1\end{array} \\ =5\left(4\right)-5\left(1\right)+5\left(1\right)-5\left(4\right) \\ =20-5+5-20 \end{gathered}$$

Solve further as:

W=0 J

Hence, the value of the work done is 0 J.

We can find the work done by using the given data in equation (i) as follows:

$$\begin{gathered} W={∫}_1^{4}2xdx+{∫}_4^1-2xdx \\ =\left[2\frac{x^2}{2}\right]\begin{array}{c}4\\ 1\end{array}+\left[-2\frac{x^2}{2}\right]\begin{array}{c}4\\ 1\end{array} \\ =4^2-1^2+\left[-\left(1^2\right)-{\left(-4\right)}^2\right] \\ =16-1+\left[-1+16\right] \end{gathered}$$

Solve further as:

W=30 J

Hence, the value of the work done is 30 J.

We can find the work done by using the given data in equation (i) as follows:

$$\begin{gathered} W={∫}_1^{4}3xdx+{∫}_4^{1}3xdx \\ =\left[3\frac{x^2}{2}\right]\begin{array}{c}4\\ 2\end{array}+\left[3\frac{x^2}{2}\right]\begin{array}{c}1\\ 4\end{array} \\ =\frac{3}{2}×1^2-\frac{3}{2}×4^2+\frac{3}{2}×1^2-\frac{3}{2}×4^2 \\ =0J \end{gathered}$$

Hence, the value of the work done is 0 J.

As the value of the work done in parts (b) and (d) is$W_{net}=0J$

Hence, the forces in part b and d are conservative.